You probably know that heavy metals—like lead, cadmium, mercury and arsenic—sometimes crop up in our food and water. While some of those metals occur naturally in our soil and waterways, they can also be intensified by past industrial uses and pollution.

Fortunately, the U.S. Food & Drug Administration tests for heavy metals in our food—but water can make things a little more complicated. If you have municipal water, your city or town should be testing it regularly for contaminants. But if you have a private well or an older house with lead plumbing, there’s a chance that your water could contain an unhealthy amount of heavy metals—and that’s where risk comes in. For kids especially, significant exposure to lead can become dangerous.

Since researchers are always looking for ways to reduce human exposure to toxins, researchers from Northwestern University thought outside the box and tested whether steeped tea could filter heavy metals from the water. They published their findings this week in ACS Food Science & Technology. Let’s see what they found.

How Was This Study Conducted?

To conduct the study, researchers tested several types of “true” teas—black, green, oolong and white—as well as chamomile and rooibos. They included both loose-leaf teas and commercially-bagged teas. 

Water samples were purposely contaminated with known amounts of metals—lead, chromium, copper, zinc and cadmium—and heated to just below boiling temperature. Tea was then steeped for various amounts of time—from just a few seconds up to 24 hours. After steeping, the amount of metal left in each water—now tea—sample was measured. 

In addition to testing teas, researchers also wanted to know if the tea bags had any effect on absorbing contaminants in the water. For this phase, they tested empty tea bags made of cotton, nylon or cellulose. 

What Did This Study Find?

Regarding the tea bags, researchers found that the cotton and nylon bags removed almost no heavy metals. The cellulose bags, however, worked incredibly well. Researchers surmise that this probably has something to do with the surface area of the cellulose bags. The more surface area available for the metal ions to stick to, the better. Cellulose is a natural biodegradable material made from wood pulp, and it provides a more textured surface than sleeker synthetic materials, like nylon. 

Nylon presents another issue, though. “Nylon tea bags are already problematic because they release microplastics,” says Benjamin Shindel, a Northwestern doctoral student and one of the study’s authors in a press release. Shindel adds that most of the tea bags used today are made from natural materials, like cellulose, and while they may release micro-particles of cellulose into our bodies, our bodies can handle it because it’s a natural material. 

Regarding the tea itself, researchers found that compared to whole tea leaves, finely ground tea leaves absorbed slightly more metal ions. Like the tea bags, researchers credit this to higher surface area in ground tea leaves compared to whole leaves. They also discovered that black tea seemed the most efficient for removing heavy metals from the water.

“When tea leaves are processed into black tea, they wrinkle and their pores open,” explains Shindel. “Those wrinkles and pores add more surface area. Grinding up the leaves also increases surface area, providing even more capacity for binding.”

In addition to the type and grind of the tea, steeping time ended up being the most significant factor in the tea leaves’ ability to bind to metal ions. The longer the steeping time, the more metal was removed. Shindel notes that steeping your tea bag for a few seconds won’t do much to remove the metal. But steeping it longer and even overnight—like if you’re making tea for iced tea—may remove most of the metal in the water.  

How Does This Apply to Real Life?

Since steeping time won the top spot in determining how much of the metal was removed from the water, regardless of what type of tea you’re brewing, allow it to steep longer. If you don’t like your tea that strong, make a larger pot with more water and allow it to sit longer. You can always reheat it if it cools down too much.

If you like using commercial tea already bagged, look for brands that use cellulose bags. Those cute, fancy pyramid bags—that usually cost more? Those are typically made with nylon, so skip those. 

If you have a hard time finding cellulose bags, you may be better off going with loose-leaf tea and a tea infuser made with high-quality stainless steel—that way, you don’t have to worry as much about heavy metals being leached out of the diffuser. Other options? An uncoated cloth tea bag with a fabric drawstring could be a solid choice. Borosilicate glass infusers and teaware don’t contain any heavy metals and are another good option.

Because tea comes from a plant, it’s loaded with inflammation-calming antioxidants. Lower inflammation may mean a reduced risk of disease, including heart disease, cancer and diabetes—so even if you’re not too concerned about your heavy metal exposure, tea can be a deliciously healthy addition to your routine.

The Bottom Line

This study suggests that tea, especially black tea, steeped for a longer time may help remove heavy metals from water. And while they note that they’re not suggesting everyone start using tea leaves as a water filter, this study does highlight some interesting possibilities for reducing heavy metals in water. 

“I’m not sure that there’s anything uniquely remarkable about tea leaves as a material,” concludes Shindell. “They have a high active surface area, which is a useful property for an adsorbent material (allowing metals to stick to it). [It’s also] what makes tea leaves good at releasing flavor chemicals rapidly into your water. But what is special is that tea happens to be the most consumed beverage in the world… With tea, people don’t need to do anything extra. Just put the leaves in your water and steep them, and they naturally remove metals.”